The intervertebral disc is important for both normal spine function, as well as for a variety of significant spine abnormalities, an important example of which is low back pain: there are 2.5 million low back injured and 1.2 million low back disabled adults in the U.S.; low back injury total compensation costs were estimated to be $2.7 billion in 1978. Critical to our understanding of this problem is the biomechanics of the intervertebral disc. We propose to further this understanding by measuring the internal deformations of the disc as a result of motion between adjacent vertebrae. No previous quantitative work has been reported on internal disc deformations other than preliminary work from this laboratory. The major goals of the proposed work are as follows: 1. For the interior of human lumbar intervertebral discs, to describe the biomechanical behavior (displacement distribution and intranuclear pressure) produced by each of 3 controlled intervertebral displacements (compression, flexion, extension), for each of 4 different disc states (normal intact, normal with annulotomy, normal denucleated, and degenerated intact), using unembalmed cadaveric excised motion segments in vitro. The measurement techniques used include a) small metallic beads implanted in a regular array within the disc, by means of a special stereotoxic instrument and hypodermic needle, b) sagittal view x- rays to record bead displacements, c) specially-designed Hall- effect transducers to record strain along the periphery of the disc, d) pressure recording from the center of the nucleus pulposus, and e) an MTS machine to impose controlled displacements upon the upper vertebra of the motion segment and to record the resulting forces. 2. For each of these 4 disc states, to compare the experimentally measured displacements to those displacements predicted by four 2-D finite element models (isotropic, orthotropic, hydrostatic, poroelastic). Each model will use as input the actual geometry of the individual disc specimens and the vertebral displacements imposed upon them. By comparing the experimental data and the model predictions several hypotheses may be tested concerning the relationship between model type and disc state.